The present invention relates to a holder for fixing a machine tool to a machine spindle, particularly holder apparatus used to fasten tightly a shank of the machine tool. In a case where a machine tool is fastened to a machine spindle, a machine tool holder is generally used as a joint device which is fixed in an axial bore of the spindle, and a straight shank of the tool or an adapter having a straight shank is inserted and tightened into a bore of the holder by threaded pins which are screwed and tightened into threaded holes provided through the wall of the holder. In the conventional fastening uniformly tightened engagement of the machine tool cannot be expected, since force for clamping the pins differs respectively with each operator. Namely, the force for clamping the pin is generally decided in accordance with respective skill of the operators on all such occasions, and there is subtle difference on strength of such force on each operator.
Also, in the conventional apparatus the fastened pin tends to loosen by vibration and or resistance of rotating or drilling operation during driving the machine tool and it would often cause some accident on the surface of the products which would be often damaged to produce an unfavorable irregular or roughened surface by the edge of the blade of the loosened tool.